Lead and intrauterine tobacco exposure may trigger ADHD.
HONOLULU -- More than 800,000 cases of attention-deficit/hyperactivity disorder in the United States may be linked to childhood exposure to lead and intrauterine exposure to tobacco smoke, according to the results of a study Dr. Tanya E. Froehlich presented at the joint meeting of the Pediatric Academic Societies.
The cross-sectional study used data from a nationally representative sample of children aged 8-15 years, which was part of the National Health and Nutrition Examination Survey (NHANES) conducted between 2001 and 2004. Data were collected from 2,588 children and their parents.
Dr. Froehlich of Cincinnati Children's Hospital Medical Center was able to determine that 9% of that sample met DSM-IV criteria for ADHD.
She looked for associations between ADHD and current blood lead levels, the reported cigarette use during pregnancy, current tobacco exposure as measured by serum cotinine levels, and household income.
In the bivariate analysis, blood lead levels, in utero tobacco smoke, and serum cotinine were all significantly associated with ADHD. However, after controlling for current tobacco exposure, age, sex, race/ethnicity, preschool attendance, maternal age at child's birth, and birth weight in a multivariate analysis, only lead and in utero tobacco smoke remained significantly associated with ADHD.
Children whose mothers reported smoking during pregnancy were 2.4-fold more likely to develop ADHD than were those whose mothers reported not smoking during pregnancy--a significant difference.
Compared with children in the first tertile of blood lead level, those in the second tertile were 1.7-fold more likely to develop ADHD. That increased to 2.3-fold for children in the third tertile. All those results were statistically significant.
In terms of absolute risk, 7% of the children whose mothers reported not smoking during pregnancy met criteria for ADHD, compared with 17% of those whose mothers did smoke during pregnancy Of those in the first tertile of blood lead levels, 5% met criteria for ADHD, compared with 9% in the second tertile and 14% in the third tertile.
Dr. Froehlich was able to determine that 35% of the current prevalent cases of ADHD in the United States could be linked to in utero tobacco exposure or to blood lead levels in the third tertile. This corresponds to 824,000 excess cases of ADHD.
"Our study is limited because it can suggest, but not prove, causal relationships because of its cross-sectional design," Dr. Froehlich said.
Furthermore, the investigators "were unable to adjust for important confounders such as in utero alcohol exposure and parental psychopathology. But I should point out that a prior smaller study that did adjust for these confounders still found significant relationships between lead, in utero tobacco exposure, and ADHD," she commented.
Dr. Froehlich stated that she had no conflicts of interest related to her presentation.
BY ROBERT FINN
San Francisco Bureau
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|Title Annotation:||Behavioral Consult|
|Date:||Jul 1, 2008|
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